1. Field of the Invention
The present invention relates to a method and to devices which are suitable for executing said method for transmitting data between a central control device of a passenger protection system in a vehicle and at least one decentralized sensor unit. In this case, the decentralized sensor unit has a sensor which records sensor measurement data. The sensor unit can be operated in a normal operating mode or in a test operating mode, wherein sensor measurement data is transferred in a normal operating mode whereas characteristic data of the sensor unit is transferred in a test operating mode. In both operating modes, the data which is transferred by the sensor unit is transferred in the form of binary encoded data packets. The transfer by the sensor unit of the data packets which are awaiting transmission follows a most recently detected synchronization pulse of the control device which periodically outputs such synchronization pulses as a request for data packets.
Such a method and suitable devices for it are disclosed in the unexamined German application DE 196 09 290 A1, for example. Said application describes a sensor module (11) which is connected to a control device (5) via a data line (1a). The sensor module (11) includes an acceleration-sensitive sensor and transfers a binary data packet, which is obtained from the sensor measured values of the sensor, periodically every 500 μs to the control device (5) with the aid of modulated current pulses as soon as it has detected a synchronization voltage pulse on the line (1a) (e.g. column 1, line 66 to column 2, line 30 or column 4, lines 55 to 62 in said document). In a second and significantly slower communication mode, it is possible to transfer test data and characteristic data of the decentralized sensor module (11) to the control device (5), e.g. initial test data of the sensor module (11) for checking that it is capable of functioning correctly, identification data of the sensor module (11) etc. (column 4, line 67 to column 5, line 13 in said document). The release readiness of a passenger protection means e.g. a side airbag which is connected to the control device (5) in this case is not yet established at this time point, since the sensor module (11) is still in a startup phase after a switching on of the supply voltage (column 5, lines 3 to 5 in said document).
It is extremely important for each passenger protection system in a vehicle that a control device forming part of said system can distinguish whether the decentralized sensor unit which is connected to it via e.g. a data line is currently operated in a test mode, e.g. initially after a switching on of its supply voltage, and is therefore transferring only characteristic data such as e.g. identification data or test data of the sensor unit or electronics, or whether the sensor unit is already in its normal operating mode wherein sensor measured values are transferred which are possibly evaluated in an algorithm and possibly give cause for triggering a passenger protection means in the event of a detected collision accident of the vehicle.